A technique has been developed to plate metal derived from a metal carbonyl gas onto a porous substrate. See U.S. Pat. No. 5,145,716.
In a practical application of the aforementioned technique, nickel is plated into the interstices of a polymeric foam. The treated foam is utilized in nickel cadmium energy cells.
Measuring the amount of deposited nickel per unit area of foam provides critical information for both foam plating process control and quality assurance. In the past, this information was obtained by curing small samples and weighing them on an analytical balance. Some non-destructive measurement methods such as electrical conductivity, light transmission, air pressure drop or infrared absorption were also tried, but with limited success. The measurement accuracy of these techniques was lower than required for acceptable quality control. The main sources of error were in the thickness and pore size variation. With electrical conductivity, the errors were caused by edge effects and density non-uniformity which affected the test current distribution.
A dependable method of determining the mount of nickel per unit area is by using a nuclear density gauge. This technique involves passing rays of beta or gamma radiation through the sample and measuring the amount of transmitted radiation. Such system are commercially available but at a relatively high cost.
The instant invention utilizes a load cell to generate a signal that is translated into a quantifiable density reading.
Load cells have been used to detect the presence of metallic components in products. See, for example, U.S. Pat. Nos. 4,866,383 and 5,034,690. Also, U.S. Pat. No. 4,232,265 senses the relative movement of two plates via the use of a strain gauge. However, the aforementioned patents do not measure the density of magnetic foams.